1. Field of the Invention
The present invention relates to a solid state imaging device with a charge transfer section, such as a CCD, and an imaging apparatus including a solid state imaging device.
2. Description of the Related Art
In a known CCD solid state imaging device, each horizontal transfer electrode extends to the outside of the channel region of a horizontal CCD register and is connected to a bus line by a contact in the outside of the channel region.
Generally, the bus line is formed of metal, such as aluminum.
In addition, in the recent CCD solid state imaging device, a configuration is proposed in which a horizontal transfer electrode is formed of a polycrystalline silicon layer of a single layer.
FIG. 10 shows an enlarged plan view near a horizontal transfer register of the CCD solid state imaging device in which the horizontal transfer electrode is formed of the polycrystalline silicon layer of a single layer. In addition, FIG. 11 is a cross-sectional view taken along the line X-X′ of FIG. 10.
As shown in FIGS. 10 and 11, a horizontal transfer register 63 is formed near a surface of a portion of a semiconductor substrate 61 other than an element separation layer 62. A horizontal transfer electrode 65 made of polycrystalline silicon is formed on the semiconductor substrate 61 with a gate insulating layer 64 interposed therebetween. To the horizontal transfer electrode 65, a horizontal transfer pulse φH1 of a first phase and a horizontal transfer pulse φH2 of a second phase are applied alternately.
In FIG. 10, a bus line 68 for supplying the horizontal transfer pulse φH2 of a second phase is disposed in a lower portion than the horizontal transfer register 63, and a bus line 67 for supplying the horizontal transfer pulse φH1 of a first phase is disposed in a lower portion than the bus line 68. The bus lines 67 and 68 are electrically connected to the horizontal transfer electrode 65 by a contact section 66.
On the horizontal transfer register 63, a light shielding layer 69 is formed so as to cover the horizontal transfer electrode 65.
In the configuration of the CCD solid state imaging device shown in FIGS. 10 and 11, it is necessary to provide a region only for connection between the horizontal transfer electrode 65 and the bus lines 67 and 68 outside the horizontal transfer register 63. This is disadvantageous in that the chip area increases.
In addition, due to extending the horizontal transfer electrode 65 to the region only for connection, the load capacitance between the horizontal transfer electrodes 65 or between the horizontal transfer electrode 65 and the light shielding layer 69 increases. As a result, the resistance from the horizontal transfer electrode 65 of a portion on the horizontal transfer register 63 to the bus lines 67 and 68 increases.
In this case, since the speed of a horizontal transfer driving pulse is decreased, an improvement of speed of horizontal charge transfer or a reduction in power consumption becomes difficult and this may lead to deterioration of horizontal transfer.
As a technique for solving these problems, there is a technique of performing connection between a horizontal transfer electrode and a bus line on a horizontal CCD register (see Japanese Patent No. 2606001 or JP-B-7-87244).
This is a technique of connecting the bus line formed of metal with the horizontal transfer electrode formed of polycrystalline silicon on a channel of the horizontal CCD register, that is, on an active region.
In such a technique, however, potential shift occurs because there is a large difference between the work functions of metal and polycrystalline silicon (see ‘Kazuya Yonemoto, Hideshi Abe “Two-million pixel FIT-CCD image sensor for HDVT”, The Institute of Electronic and Information Engineers of Japan, VLD90-22, ICD90-58, June 1990’).